Persuasive speech: Breastfeeding

New Evidence on Breastfeeding and Postpartum Depression: The Importance of Understanding Women’s Intentions Cristina Borra •Maria Iacovou •Almudena Sevilla Published online: 21 August 2014 The Author(s) 2014. This article is published with open access at Springerlink.com AbstractThis study aimed to identify the causal effect of breastfeeding on postpartum depression (PPD), using data on mothers from a British survey, the Avon Longitudinal Study of Parents and Children. Multivariate linear and logistic regressions were performed to investigate the effects of breastfeeding on mothers’ mental health measured at 8 weeks, 8, 21 and 32 months postpartum. The estimated effect of breastfeeding on PPD differed according to whe- ther women had planned to breastfeed their babies, and by whether they had shown signs of depression during preg- nancy. For mothers who were not depressed during preg- nancy, the lowest risk of PPD was found among women who had planned to breastfeed, and who had actually breastfed their babies, while the highest risk was found among women who had planned to breastfeed and had not gone on to breastfeed. We conclude that the effect of breastfeeding on maternal depression is extremely heterogeneous, being mediated both by breastfeeding intentions during pregnancy and by mothers’ mental health during pregnancy. Our resultsunderline the importance of providing expert breastfeeding support to women who want to breastfeed; but also, of providing compassionate support for women who had intended to breastfeed, but who nd themselves unable to.

KeywordsBreastfeeding Mental health Edinburgh postnatal depression scale Child development ALSPAC Introduction Approximately 13 % of women experience postpartum depression (PPD) within the 14 weeks after giving birth [1]. If the antenatal period is also considered, as many as 19 % of women experience a depressive episode during pregnancy or the rst 3 months postpartum [2]. Post-natal depression has an immediate impact on mothers and carries long-term risks for mothers’ future mental health [3,4]; it also has signi cant negative effects on the cognitive, social and physical development of their children [5,6]. In addition, post-natal depression involves substantial eco- nomic costs, in terms of costs to healthcare systems [7] and losses in productivity via maternal absenteeism from work, premature retirement, and long-term unemployment [8].

The effect of breastfeeding on the risk of PPD is not well understood. Several studies have demonstrated an associ- ation between longer breastfeeding durations and a lower prevalence of PPD [9–14]. However, other studies have suggested the opposite, namely that breastfeeding mothers are at increased risk of PPD [15,16]; or found no associ- ation [17,18]. Of those studies which suggest bene cial effects from breastfeeding, several have relied on small samples, and few have controlled for potential confounders such as socioeconomic factors (maternal education, family income, marital status), the quality of relationships (marital C. Borra (&) Facultad de Ciencias Econo´ micas y Empresariales, University of Seville, Ramo´ n y Cajal 1, 41018 Seville, Spain e-mail: [email protected] M. Iacovou Department of Sociology, University of Cambridge, Free School Lane, Cambridge CB2 3RQ, UK e-mail: [email protected] M. Iacovou ISER, University of Essex, Colchester CO4 3SQ, UK A. Sevilla Queen Mary University of London, Mile End Road, London E1 4NS, UK e-mail: [email protected] 123 Matern Child Health J (2015) 19:897–907 DOI 10.1007/s10995-014-1591-z stability, social networks), and stressful life events [19,20].

Thus, it has been extremely dif cult to identify whether the observed relationships are causal, as opposed to arising because breastfeeding is more likely to be practiced by mothers whose characteristics are themselves associated with a lower risk of depression [21–23]. Additionally, as Ip et al. [24] have pointed out, most existing studies have not controlled for pre-existing mental health conditions.

Thus, the extent to which breastfeeding in uences mental health, as opposed to mental health driving the incidence and duration of breastfeeding, has not been clear.

The aim of the current study is to examine explicitly whether breastfeeding affects maternal mental health out- comes. Speci cally, we examine the hypothesis that the relationship between breastfeeding and maternal mental health is mediated by the mother’s intention to breastfeed.

The relationship between breastfeeding and maternal mental health may be driven by biological factors, such as differences in hormone levels between breast- and formula- feeding mothers [25]; if maternal mental health is also affected by mothers’ feelings of success or failure in relation to their original plans and aspirations, we may expect the intention to breastfeed to play a crucial role.

Data and Methods Data and Key Variables This research is based on data from the Avon Longitudinal Survey of Parents and Children (ALSPAC), a survey of around 14,000 children born in the Bristol area of England in the early 1990s [26]. Mothers were recruited into the survey by doctors, at the point when they rst reported their pregnancy. Data were collected by questionnaires admin- istered to both parents at four points during pregnancy and at several stages following birth.

Details of all data collected in the ALSPAC survey are available on the study website through a fully searchable data dictionary [27]. Our study obtained ethical approval from the ALSPAC Law and Ethics Committee and the Local Research Ethics Committees.

We used a sample of mothers whose children form the ‘‘core sample’’ of ALSPAC. This sample consists of 14,541 pregnancies which resulted in 14,676 known foetuses; there were 14,062 live births, and 13,988 babies surviving to 1 year. We employed a maximizing strategy with respect to sample size, using as many observations as possible to analyse each outcome-effect dyad. Sample sizes thus vary slightly between regressions. The experiences of mothers and babies following pre-term births, or separation due to NICU care, may differ from the experiences of other mothers and babies. We do not exclude these mother/babypairs from our sample, but have checked that our results do not change if they are excluded; these results are available from the authors on request.

As a measure of depression, the Edinburgh Postnatal Depression Scale (EPDS) was used. The EPDS, designed by Cox et al. [28] to screen for PPD, was collected during pregnancy at 18 and 32 weeks’ gestation, and post-natally at 8 weeks, and 8, 18, and 33 months. The EPDS is the most frequently used screening questionnaire for PPD; the EPDS is sensitive to changes in depression over time, and has been demonstrated to be a valid and reliable tool for the measurement of both postpartum and antenatal depression [29,30]. The instrument consists of 10 questions, each with four possible answers describing symptoms of increasing severity or duration; aggregate scores on the EPDS range from 0 to 30. The authors of the EPDS have suggested that women should be referred to a mental health specialist if they score 13 or higher during the post-partum period [31] and 15 or more during pregnancy [32]. Therefore, we constructed indicators of depressive symptomatology, de ned as EPDS[14 in pre-natal assessments and EPDS [12 in postpartum assessments.

Mothers were asked during pregnancy how they intended to feed their babies for the rst 4 weeks. Following their child’s birth, they were asked at several points how they were actually feeding, and the ages at which infant formula and solid foods were introduced. Using this information, we computed seven binary indicators: (1) initiation (putting the baby to the breast at least once); (2–4) any breastfeeding for at least 1, 2 and 4 weeks respectively; and (5–7) exclusive breastfeeding for at least 1, 2 and 4 weeks respectively. We also computed two continuous indicators: total duration of breastfeeding and total duration of exclusive breastfeeding; results for these contin- uous indicators are similar to results obtained using the binary indicators, and are available from the authors on request.

Analysis We estimate multivariate logistic regressions, presenting odds ratios and 95 % con dence intervals. All hypotheses are tested using two-tailedp values\0.05.

We present estimates from three speci cations. Model A controls only for the child’s sex and parental education.

Model B additionally controls for other socio-demographic variables, and information on pregnancy and birth. Finally, Model C includes information on the mother’s physical and mental health, including antenatal EPDS assessments, together with factors relating to the quality of interpersonal relationships and stressful life events (see Table6in the Appendix for precise de nitions of these variables). Thus, Model A provides a rst approximation to the associations of interest, Model B estimates these relationships net of a range of potential confounders, while Model C aims to estimate 898Matern Child Health J (2015) 19:897–907 123 causal relationships as accurately as possible by eliminating potential reverse causality arising from the fact that previ- ously depression-prone mothers may be less likely to decide to breastfeed, or to breastfeed for shorter durations.

After conducting this analysis for the whole sample, we split the sample into mothers who were, and who were not, depressed during pregnancy; for each group, we examine differences in outcomes between women who had planned to breastfeed, and women who had not.

Results Study Variables Descriptive statistics for variables of interest are shown in Table1. The prevalence of antenatal depression, using a cut-off of EPDS[14, is 7 % at 18 weeks’ pregnancy and 8 % at 32 weeks, similar to rates reported in previous studies [33]. Rates of PPD were between 9 and 12 %, also similar to results from former analyses [34].80 % of mothers in this sample initiated breastfeeding and 74 % breastfed for 1 week or more. By 4 weeks only 56 % of mothers were breastfeeding at all and only 43 % were breastfeeding exclusively. The percentages of women feeding for the different durations considered are shown in Table1; mean durations for breastfeeding and exclusive breastfeeding are also shown.

Table2shows the raw relationships between postnatal depressive symptomatology, and (a) prenatal depression, and (b) different measures of breastfeeding duration. A signi cant degree of correlation is present between post- natal and antenatal EPDS scores; a clear negative rela- tionship also exists between symptoms of maternal depression measured at 8 weeks, and breastfeeding dura- tion. The association between depression and breastfeeding is always negative, but generally statistically insigni cant, at 8, 21 and 33 months.

Sample Characteristics Socio-demographic characteristics for sample members are presented in Table7in the Appendix. The mean age of participants was 28.3 years (SD=4.8). 95 % of the women were white, 86 % were married, 13 % had university degrees, while a further 22 % had high school quali cations at age 18 (‘‘A’’ levels); and 74 % owned the house in which they lived. In relation to pregnancy and birth, 64 % felt usually well, 55 % percent were working while pregnant, 45 % were primiparous, and only 9 % delivered via Cesar- ean section. The average gestational age was 39.5 weeks (SD=1.8). 48 % of mothers and 37 % of fathers had themselves been breastfed as babies. 28 % of the pregnan- cies were unplanned; 15 % of mothers had lived through their own parents’ divorce before their eighteenth birthday.

Table3presents the results of logistic regressions esti- mating the effect of breastfeeding on PPD.

As explained earlier, three models are estimated: Model A controls only for the child’s sex and parental education; Model B controls in addition for a wide range of socio- economic and demographic factors, plus information on pregnancy and birth; and Model C also controls for mother’s health (including mental health) in pregnancy, relationship quality and stressful life events.

We consider four different outcomes: EPDS[12 mea- sured at 8 weeks, 8, 21 and 33 months postpartum. For each model/outcome dyad, the model is estimated seven times, for seven different measures of breastfeeding (ini- tiation; any breastfeeding for at least 1, 2 and 4 weeks; and exclusive breastfeeding for at least 1, 2 and 4 weeks).

Thus, each coef cient in Table3comes from a separate regression.

At 8 weeks postpartum, we observe a pronounced relationship between breastfeeding and PPD, under both Table 1Descriptive statistics for variables of interest N mean s.d.

Maternal mental health during pregnancy At risk of antenatal depression, 18 weeks (EPDS[14)10,904 7 % (0.3) At risk of antenatal depression, 32 weeks (EPDS[14)11,305 8 % (0.3) Maternal mental health post-partum At risk of postpartum depression, 8 weeks (EPDS[12)10,756 10 % (0.3) At risk of postpartum depression, 8 months (EPDS[12)10,345 8 % (0.3) At risk of postpartum depression, 21 months (EPDS[12)9,605 10 % (0.3) At risk of postpartum depression, 33 months (EPDS[12)8,985 12 % (0.3) Breastfeeding Mother intended to breastfeed 11,547 65 % (0.5) Initiated breastfeeding 11,012 80 % (0.4) Breastfed for 1 week 10,668 74 % (0.4) Breastfed for 2 weeks 10,680 68 % (0.5) Breastfed for 4 weeks 10,972 56 % (0.5) Duration of any breastfeeding (months) 8,317 5.17 (4.7) Exclusively breastfed for 1 week 10,668 64 % (0.5) Exclusively breastfed for 2 weeks 10,680 60 % (0.5) Exclusively breastfed for 4 weeks 10,972 43 % (0.5) Duration of exclusive breastfeeding (months)8,726 1.31 (1.2) Figures in the middle column are means in the case of continuous variables, and percentages of the sample in the case of dichotomous variables Matern Child Health J (2015) 19:897–907899 123 Models A and B. The odds ratios for these models indicate that longer durations of breastfeeding are associated with larger reductions in the risk of PPD, and exclusive breastfeeding is associated with a larger reduction than any breastfeeding. However, under Model C, when we control for mothers’ health during pregnancy, these effects largely disappear; the only signi cant relationship which remains comes from exclusive breastfeeding for 4 weeks or longer (OR 0.81, 95 % CI 0.68, 0.97).

The relationship between breastfeeding and PPD is also weaker, the later the EPDS score is assessed; at 8 months postpartum and thereafter, most of the estimated coef - cients are not signi cantly different from zero (indeed, a few of the results are counter-intuitive, suggesting that breastfeeding may bepositivelyrelated to an increased risk of depression measured at 33 months postpartum).

Thus, for the sample as a whole, our results demonstrate little evidence for a causal relationship between breastfeeding and the risk of PPD. In the next section, we investigate the possibility that the relationship between breastfeeding and depression varies according to two factors: whether mothers were assessed as at risk of depression during pregnancy, and whether they had been planning to breastfeed their babies. We show that the relationship between breastfeeding and depression is indeed highly heterogeneous, and that this fact explains why little effect is found when considering women as a homogeneous group.

Heterogeneous Effects by Mental Health During Pregnancy and Breastfeeding Intention We re-estimated Model C separately for mothers who were, and who were not, depressed during pregnancy (interms of having a score EPDS[14 at least once during pregnancy). As before, we estimated regressions separately for each time at which postnatal depression was assessed (8 weeks, and 8, 21 and 33 months postpartum); for each of these time periods, we estimated seven models, one for each discrete measure of breastfeeding. However, instead of simply controlling for whether or not mothers breastfed for the relevant duration, we identify four groups of women, by whether they hadplannedto breastfeed, and whether they hadactuallybreastfed for the relevant dura- tion. These four groups are:

•Mothers whohad notplanned to breastfeed, and who did notbreastfeed (reference group) •Mothers whohad notplanned to breastfeed, but who didactually breastfeed •Mothers whohadplanned to breastfeed, but whodid notactually breastfeed •Mothers whohadplanned to breastfeed, and whodid actually breastfeed Each regression thus generates three coef cients of interest; these coef cients are expressed as odds ratios, relative to the reference group.

Table4presents results for motherswithoutprenatal depression symptoms. Column (2) displays odds ratios and con dence intervals for mothers who did not plan to breastfeed, but who did actually breastfeed; column (3) indicates whether these mothers are signi cantly different from the mothers in the reference group.

Column (4) presents odds ratios for mothers who planned to breastfeed but who did not breastfeed for the relevant duration; Column (5) present odds ratios for mothers who Table 2Raw correlations between study variables Postpartum EPDS scores Postnatal EPDS[12 Postnatal EPDS[12 Postnatal EPDS[12 Postnatal EPDS[12 at 8 weeks at 8 months at 21 months at 33 months Maternal mental health during pregnancy Antenatal EPDS[14 at 18 weeks 0.279*** 0.220*** 0.216*** 0.207*** Antenatal EPDS[14 at 32 weeks 0.350*** 0.309*** 0.288*** 0.271*** Breastfeeding measures Initiated breastfeeding-0.034**-0.027*-0.018-0.018 Breastfed for 1 week or more-0.037**-0.021-0.019-0.015 Breastfed for 2 weeks or more-0.038**-0.023-0.015-0.010 Breastfed for 4 weeks or more-0.037**-0.011-0.005-0.005 Duration of any breastfeeding-0.044***-0.021-0.020-0.009 Exclusively breastfed for 1 week or more-0.041***-0.019-0.023-0.022 Exclusively breastfed for 2 weeks or more-0.040***-0.033**-0.018-0.026* Exclusively breastfed for 4 weeks or more-0.052***-0.021-0.016-0.013 Duration of exclusive breastfeeding-0.036**-0.025-0.021- 0.014 Pvalues are indicated by asterisks, with *P\0.05, **P\0.01, ***P\0.001 900Matern Child Health J (2015) 19:897–907 123 planned to breastfeed, and who did breastfeed for the rele- vant duration. Column (6) indicates whether the odds ratios in Column (4) and (5) are signi cantly different from each other. Thus, the test results in Column (3) indicate whether breastfeeding makes a difference in the case of women whodid not originally plan to breastfeed, while the tests in Col- umn (6) indicate whether breastfeeding makes a difference in the case of mothers who had planned to breastfeed.

The strongest result from Table4is that breastfeeding is strongly associated with a lower risk of depression at Table 3Results from logistic regressions: effects of breastfeeding on postpartum depression Model A Adjusted OR [95 % CI]Model B Adjusted OR [95 % CI]Model C Adjusted OR [95 % CI] Dependent variable: EPDS[12 at 8 weeks Breastfeeding initiated 0.87 [0.74,1.03] 1.06 [0.88,1.27] 1.1 [0.89,1.37] Any b/f, 1 week?0.8 [0.69,0.93]** 0.95 [0.80,1.13] 1.08 [0.88,1.33] Any b/f, 2 weeks?0.83 [0.71,0.96]* 0.93 [0.78,1.09] 0.98 [0.81,1.19] Any b/f, 4 weeks?0.77 [0.67,0.89]*** 0.81 [0.70,0.95]** 0.88 [0.74,1.06] Exclusive b/f, 1 week?0.8 [0.70,0.92]** 0.91 [0.78,1.06] 0.99 [0.82,1.19] Exclusive b/f, 2 weeks?0.78 [0.68,0.90]*** 0.85 [0.73,0.99]* 0.89 [0.74,1.06] Exclusive b/f, 4 weeks?0.73 [0.64,0.85]*** 0.75 [0.64,0.88]*** 0.81 [0.68,0.97]* N 10,509–10,546 10,393–10,428 9,722–9,757 Dependent variable: EPDS[12 at 8 months Breastfeeding initiated 0.86 [0.72,1.03] 1.01 [0.83,1.23] 0.99 [0.79,1.24] Any b/f, 1 week?0.9 [0.76,1.07] 1.04 [0.86,1.25] 1.15 [0.93,1.43] Any b/f, 2 weeks?0.88 [0.75,1.03] 0.98 [0.82,1.17] 1.02 [0.84,1.25] Any b/f, 4 weeks?0.89 [0.76,1.04] 0.95 [0.81,1.13] 1.05 [0.87,1.28] Exclusive b/f, 1 week?0.92 [0.79,1.07] 1.02 [0.86,1.21] 1.12 [0.92,1.36] Exclusive b/f, 2 weeks?0.83 [0.71,0.97]* 0.9 [0.76,1.06] 0.93 [0.77,1.12] Exclusive b/f, 4 weeks?0.86 [0.74,1.00] 0.9 [0.76,1.06] 1.02 [0.84,1.23] N 10,080–10,116 9,258–9,999 9,354–9,388 Dependent variable: EPDS[12 at 21 months Breastfeeding initiated 0.93 [0.78,1.11] 1.08 [0.89,1.32] 1.09 [0.87,1.37] Any b/f, 1 week?0.97 [0.82,1.15] 1.14 [0.94,1.38] 1.26 [1.02,1.56]* Any b/f, 2 weeks?1 [0.86,1.18] 1.11 [0.93,1.33] 1.19 [0.97,1.46] Any b/f, 4 weeks?0.99 [0.85,1.14] 1.03 [0.87,1.21] 1.15 [0.95,1.38] Exclusive b/f, 1 week?0.93 [0.80,1.08] 1.04 [0.88,1.23] 1.19 [0.98,1.44] Exclusive b/f, 2 weeks?0.96 [0.82,1.11] 1.03 [0.87,1.21] 1.11 [0.92,1.33] Exclusive b/f, 4 weeks?0.9 [0.77,1.04] 0.92 [0.79,1.08] 1.06 [0.88,1.27] N 9,370–9,406 9,258–9,929 8,704–8,737 Dependent variable: EPDS[12 at 33 months Breastfeeding initiated 1.04 [0.88,1.24] 1.22 [1.01,1.48]* 1.22 [0.98,1.51] Any b/f, 1 week?1.01 [0.86,1.18] 1.16 [0.97,1.39] 1.27 [1.04,1.55]* Any b/f, 2 weeks?1.02 [0.87,1.18] 1.13 [0.95,1.33] 1.19 [0.99,1.44] Any b/f, 4 weeks?1.01 [0.88,1.16] 1.07 [0.92,1.25] 1.17 [0.98,1.39] Exclusive b/f, 1 week?0.92 [0.80,1.06] 1.01 [0.86,1.18] 1.09 [0.92,1.30] Exclusive b/f, 2 weeks?0.9 [0.78,1.03] 0.96 [0.82,1.11] 0.99 [0.84,1.18] Exclusive b/f, 4 weeks?0.95 [0.83,1.09] 0.98 [0.85,1.14] 1.1 [0.93,1.29] N 8,704–8,805 8,676–8,706 8,172–8,202 Coef cients are expressed as odds ratios and 95 % con dence intervals. Each estimated coef cient comes from a different regression. Model A controls for the child’s sex and parental education. Model B additionally controls for pregnancy and birth information; child characteristics at birth; demographic and socio-economic variables; and breastfeeding attitudes. Model C also controls for mother’s health in pregnancy, inter- personal relationships, and stressful life events (see Table6in the Appendix). Sample sizes vary slightly between regressions; the range of N is given in each panel P values are indicated by asterisks, with *P\0.05, **P\0.01, ***P\0.001 Matern Child Health J (2015) 19:897–907901 123 Table 4Results from logistic regressions: effects of breastfeeding on postpartum depression (mothers not at risk of depression during pregnancy) Dependent variable (1) Didn’t plan to breastfeed, didn’t breastfeed (reference group)(2) Didn’t plan to breastfeed, did breastfeed(3) Difference between coeffs (1) and (2)(4) Planned to breastfeed, didn’t breastfeed(5) Planned to breastfeed, did breastfeed(6) Difference between coeffs (4) and (5) EPDS[12 at 8 weeks (N=8,629–8,597) Breastfeeding initiated – 1.24 [0.88, 1.75] 2.55 [1.34,4.84] 0.36 [0.18, 0.71] *** Any b/f, 1 week?– 1.33 [0.92, 1.92] 1.60 [0.97, 2.63] 0.54 [0.30, 0.96] ** Any b/f, 2 weeks?– 1.43 [0.98, 2.09] 1.44 [0.96, 2.16] 0.56 [0.33, 0.94] ** Any b/f, 4 weeks?– 1.26 [0.82, 1.94] 1.31 [0.96, 1.78] 0.61 [0.37, 1.01] ** Exclusive b/f, 1 week?– 1.34 [0.91, 1.97] 1.45 [1.00, 2.09] 0.58 [0.35, 0.95] ** Exclusive b/f, 2 weeks?– 1.30 [0.86, 1.96] 1.41 [1.01, 1.96] 0.58 [0.35, 0.96] ** Exclusive b/f, 4 weeks?– 1.26 [0.74, 2.14] 1.22 [0.93, 1.59] 0.66 [0.37, 1.17] * EPDS[12 at 8 months (N=8,300–8,334) Breastfeeding initiated – 0.75 [0.51, 1.09] 1.37 [0.62, 3.03] 1.09 [0.46, 2.55] Any b/f, 1 week?– 0.89 [0.59, 1.35] 1.02 [0.57, 1.84] 1.37 [0.69, 2.72] Any b/f, 2 weeks?– 0.87 [0.56, 1.36] 1.47 [0.97, 2.24] 0.92 [0.52, 1.63] Any b/f, 4 weeks?– 0.80 [0.47, 1.34] 1.32 [0.95, 1.85] 1.13 [0.62, 2.03] Exclusive b/f, 1 week?– 1.00 [0.64, 1.55] 1.39 [0.94, 2.06] 0.95 [0.55, 1.66] Exclusive b/f, 2 weeks?– 0.77 [0.47, 1.26] 1.59 [1.13, 2.24] 0.93 [0.53, 1.66] Exclusive b/f, 4 weeks?– 0.66 [0.33, 1.31] 1.30 [0.97, 1.73] 1.49 [0.72, 3.08] EPDS[12 at 21 months (N=7,751–7,787) Breastfeeding initiated – 1.16 [0.82, 1.64] 1.67 [0.80, 3.48] 0.56 [0.26, 1.21] Any b/f, 1 week?– 1.44 [1.00, 2.08] * 0.87 [0.49, 1.55] 0.95 [0.50, 1.81] Any b/f, 2 weeks?– 1.62 [1.12, 2.36] * 1.18 [0.77, 1.80] 0.64 [0.38, 1.08] Any b/f, 4 weeks?– 1.61 [1.07, 2.43] * 1.16 [0.84, 1.59] 0.61 [0.38, 1.00] * Exclusive b/f, 1 week?– 1.49 [1.02, 2.18] * 1.00 [0.68, 1.48] 0.80 [0.48, 1.33] Exclusive b/f, 2 weeks?– 1.34 [0.90, 2.01] 1.08 [0.77, 1.52] 0.79 [0.48, 1.29] Exclusive b/f, 4 weeks?– 1.32 [0.79, 2.20] 1.07 [0.82, 1.40] 0.77 [0.44, 1.34] EPDS[12 at 33 months (N=7,300–7,330) Breastfeeding initiated – 1.12 [0.81, 1.55] 1.32 [0.63, 2.75] 0.92 [0.42, 1.98] Any b/f, 1 week?– 1.24 [0.89, 1.74] 1.27 [0.79, 2.06] 0.87 [0.50, 1.50] Any b/f, 2 weeks?– 1.45 [1.02, 2.05] * 1.60 [1.11, 2.32] 0.62 [0.39, 0.99] ** Any b/f, 4 weeks?– 1.23 [0.83, 1.82] 1.28 [0.96, 1.71] 0.87 [0.55, 1.38] Exclusive b/f, 1 week?– 1.31 [0.91, 1.87] 1.54 [1.11, 2.14] 0.66 [0.42, 1.04] ** Exclusive b/f, 2 weeks?– 1.15 [0.78, 1.68] 1.59 [1.18, 2.13] 0.68 [0.43, 1.07] ** Exclusive b/f, 4 weeks?– 1.05 [0.64, 1.73] 1.25 [0.97, 1.59] 1.02 [0.60, 1.75] Each row presents a set of three coef cients from the same regression; these are expressed as odds ratios relative to the reference group, with 95 % con dence intervals. The coef cients in each row come from a different regression. Model C is estimated, controlling for all variables in Table6.Sample sizes vary slightly between regressions; the range of N is given in each panel Pvalues are indicated by asterisks, with *P\0.05, **P\0.01, ***P\0.001 902Matern Child Health J (2015) 19:897–907 123 8 weeks postpartum, for women who had planned to breastfeed. The odds ratios in Column 4 are all well over 1, while the odds ratios in Column 5 are all well below 1; the differences between the two are statistically signi cant at the 1 % level or better for the rst six measures of breastfeeding, and signi cant at the 5 % level for the remaining measure. The effects are smaller for later assessment periods. At 8 and 21 months, the odds ratios in Column 5 are lower than the odds ratios in Column 4 in almost all cases; however, the differences are not statisti- cally signi cant. At 33 months, the differences are larger again, and are signi cant at the 1 % level for three of the seven measures of breastfeeding.

Interestingly, among the group of mothers who had not planned to breastfeed, the risk of depression was higher among women who went on to breastfeed. These differences are statistically signi cant for depression measured at 21 months, the largest being for any breastfeeding for 2 weeks on EPDS at 21 months (OR 1.62; 95 % CI 1.12, 2.36); at 8 weeks and 33 months the coef cients are all positive, though not gen- erally signi cant at the 5 % level). To test whether our results were driven by a few mothers with very severe depressive symptoms, we repeated the analysis excluding those mothers with EPDS scores of 20 or more (the cut-off used in general practitioners’ guidelines [35] ); the results were virtually the same. We also investigated whether the effects depended on whether the mother was primiparous or multiparous, as sug- gested by [36]; again, the results were not affected.

Results for mothers who had been assessed as at risk of depression during pregnancy are shown in Table5. For this group, results are less well de ned, at least in part because of the smaller sample size. Our ndings suggest that among women who had planned to breastfeed, breastfeeding is associated with a lower risk of PPD (as for mothers not depressed during pregnancy, although with a much smaller effect). However, for previously depressed mothers, there may also be a protective effect from breastfeeding when mothers hadnotplanned to breastfeed. These results should be interpreted with caution: the only signi cant effect was found on EPDS measured at 8 weeks and for at least 4 weeks’ exclusive breastfeeding (OR 0.42; 95 % CI 0.20, 0.90).

Discussion The aim of this study was to examine whether breast- feeding in uenced the risks of postnatal depression. This study extends previous research by using a large longitu- dinal dataset; controlling for a large set of socioeconomic, relational, and psychosocial confounders; measuring maternal mood at different time points both before and after delivery; and utilising several measures of breast- feeding initiation, duration, and exclusivity.We found that the effect of breastfeeding on maternal mood differed by both maternal mental health during preg- nancy; and whether mothers intended to breastfeed. To our knowledge, this study is the rst to document this result.

For the majority of mothers who did not show symptoms of depression before birth, breastfeeding decreased the risk of PPD among mothers who had intended to breastfeed, but increased the risk of PPD among mothers who hadnot intended to breastfeed.

We also found that the bene cial effects of breastfeed- ing were strongest at 8 weeks after birth, and that the association was weaker at 8 months and onwards. This nding is in line with the ndings of the only other lon- gitudinal research in this area [37] which signi cant effects at 6 weeks but not at 12 weeks postpartum. Our results are nevertheless important, because of the established rela- tionship between depression, even in the very early post- partum period, and maternal-infant bonding [38].

Estimates for the smaller group of mothers who had shown signs of depression during pregnancy were less precise, but differed from the estimates for non-depressed women in two important ways. The protective effects of breastfeeding as planned were smaller for women who had been depressed during pregnancy; but exclusive breast- feeding for 4 weeks appeared to exercise a protective effect for this group, which it did not do for the women who had not been depressed in pregnancy.

We recognize several limitations in our analyses.

Although we employ the most commonly used measure of depressive symptomatology, we acknowledge that includ- ing a clinical diagnosis of antenatal and PPD would have increased the value of our ndings. Also, misclassi cation bias may arise when relying on self-report methods to assess breastfeeding outcomes. Thirdly, even though we use a large population-based sample with low loss to fol- low-up, sampling bias resulting from the voluntary nature of participation in the survey could have in uenced results.

For instance, we acknowledge a shortfall in the numbers of ethnic minority mothers that may limit the generalizability of the results. Finally, even though we control for many more potential confounders than any other study on the subject, there may remain some unobserved factor, for example aspects of maternal IQ or personality, which could affect the results.

In summary, the effect of breastfeeding on maternal depression symptoms was found to be highly heteroge- neous and, crucially, mediated by breastfeeding intentions during pregnancy. Our most important nding relates to the majority of mothers who were not depressed during preg- nancy, and who planned to breastfeed their babies. For these mothers, breastfeeding as planned decreased the risks of PPD, while not being able to breastfeed as planned increased the risks. These ndings have implications for Matern Child Health J (2015) 19:897–907903 123 Table 5Results from logistic regressions: effects of breastfeeding on postpartum mental health (mothers at risk of depression when pregnant) Dependent variable (1) Didn’t plan to breastfeed, didn’t breastfeed (reference group)(2) Didn’t plan to breastfeed, did acually breastfeed(3) Difference between coeffs (1) and (2)(4) Planned to breastfeed, didn’t breastfeed(5) Planned to breastfeed, did breastfeed(6) Difference between coeffs (4) and (5) EPDS[12 at 8 weeks (N=1,124–1,128) Breastfeeding initiated – 1.24 [0.79,1.94] 0.82 [0.29,2.34] 1.11 [0.37,3.33] Any b/f, 1 week?– 1.33 [0.81,2.19] 1.45 [0.74,2.84] 0.56 [0.25,1.24] Any b/f, 2 weeks?– 1.06 [0.63,1.80] 1.71 [0.95,3.07] 0.47 [0.22,1.02] ** Any b/f, 4 weeks?– 0.69 [0.37,1.28] 1.10 [0.73,1.67] 1.13 [0.54,2.35] Exclusive b/f, 1 week?– 1.14 [0.67,1.96] 1.29 [0.77,2.16] 0.67 [0.32,1.37] Exclusive b/f, 2 weeks?– 1.19 [0.68,2.09] 1.46 [0.91,2.35] 0.49 [0.24,0.99] ** Exclusive b/f, 4 weeks?– 0.42 [0.20,0.90] * 1.07 [0.74,1.53] 1.65 [0.71,3.83] EPDS[12 at 8 months (N=1,042–1,047) Breastfeeding initiated – 0.91 [0.56,1.45] 0.85 [0.28,2.55] 1.34 [0.42,4.28] Any b/f, 1 week?– 1.02 [0.60,1.72] 1.23 [0.59,2.54] 0.91 [0.38,2.14] Any b/f, 2 weeks?– 0.98 [0.56,1.71] 1.36 [0.72,2.57] 0.81 [0.36,1.84] Any b/f, 4 weeks?– 0.97 [0.52,1.83] 1.03 [0.66,1.61] 1.09 [0.51,2.32] Exclusive b/f, 1 week?– 1.00 [0.57,1.76] 1.04 [0.59,1.82] 1.12 [0.52,2.42] Exclusive b/f, 2 weeks?– 0.88 [0.49,1.60] 1.08 [0.65,1.80] 1.16 [0.54,2.47] Exclusive b/f, 4 weeks?– 0.86 [0.41,1.80] 1.06 [0.72,1.56] 1.10 [0.48,2.53] EPDS[12 at 21 months (N=941–945) Breastfeeding initiated – 1.02 [0.62,1.69] 0.32 [0.08,1.34] 3.12 [0.72,13.64] Any b/f, 1 week?– 1.07 [0.62,1.86] 0.76 [0.33,1.73] 1.26 [0.49,3.26] Any b/f, 2 weeks?– 1.11 [0.63,1.95] 1.00 [0.49,2.01] 0.91 [0.38,2.19] Any b/f, 4 weeks?– 0.84 [0.44,1.60] 0.75 [0.47,1.22] 1.68 [0.76,3.70] Exclusive b/f, 1 week?– 0.89 [0.49,1.61] 0.74 [0.40,1.36] 1.50 [0.66,3.42] Exclusive b/f, 2 weeks?– 1.03 [0.56,1.89] 0.95 [0.55,1.65] 1.01 [0.46,2.24] Exclusive b/f, 4 weeks?– 0.64 [0.30,1.37] 0.82 [0.54,1.23] 1.93 [0.82,4.56] EPDS[12 at 33 months (N–865–869) Breastfeeding initiated – 1.28 [0.76,2.15] 1.81 [0.53,6.16] 0.61 [0.17,2.18] Any b/f, 1 week?– 1.09 [0.62,1.92] 1.16 [0.53,2.55] 1.03 [0.41,2.59] Any b/f, 2 weeks?– 1.16 [0.65,2.08] 1.70 [0.88,3.30] 0.62 [0.27,1.45] Any b/f, 4 weeks?– 1.08 [0.56,2.08] 1.29 [0.80,2.08] 0.90 [0.41,1.96] Exclusive b/f, 1 week? – 1.01 [0.55,1.84] 1.33 [0.75,2.37] 0.92 [0.42,2.03] Exclusive b/f, 2 weeks?– 1.18 [0.64,2.20] 1.56 [0.92,2.65] 0.65 [0.30,1.41] Exclusive b/f, 4 weeks?– 0.97 [0.45,2.09] 1.28 [0.84,1.95] 0.97 [0.41,2.30] Each row presents a set of three coef cients from the same regression; these are expressed as odds ratios relative to the reference group, with 95 % con dence intervals. The coef cients in each row come from a different regression. Model C is estimated, controlling for all variables in Table6.Sample sizes vary slightly between regressions; the range of N is given in each panel Pvalues are indicated by asterisks, with *P\0.05, **P\0.01, ***P\0.001 904Matern Child Health J (2015) 19:897–907 123 the way in which new mothers are supported; they suggest that the provision of expert breastfeeding support may, in addition to increasing breastfeeding rates and durations, have the additional bene t of improving mental health outcomes among new mothers. At the same time, it is clear that where mothers had intended to breastfeed, not being able to breastfeed may have deleterious consequences on their risk of PPD, and that providing specialised support to new mothers who had intended to breastfeed, but who for some reason nd themselves unable to breastfeed, may also constitute a desirable health policy objective.

AcknowledgmentsThis paper has bene ted from comments pro- vided by participants at the 20th Public Economics Meeting and at the 27th Annual Conference of the European Society for Population Economics. We acknowledge comments and support from colleagues at ISER, particularly Emilia del Bono and Birgitta Rabe. We are extremely grateful to all the families who took part in this study, the midwives for their help in recruiting them, and the whole ALSPAC team, which includes interviewers, computer and laboratory techni- cians, clerical workers, research scientists, volunteers, managers, receptionists and nurses. The UK Medical Research Council and the Wellcome Trust (Grant ref: 092731) and the University of Bristol provide core support for ALSPAC. This publication is the work of the authors, who will all serve as guarantors for the contents of this paper.

This research was speci cally funded by the UK’s Economic and Social Research Council (ESRC) under research Grant RES-062-23- 1693 Effects of breastfeeding on children, mothers and employers.

The authors are independent from the ESRC.

Open AccessThis article is distributed under the terms of the Creative Commons Attribution License which permits any use, dis- tribution, and reproduction in any medium, provided the original author(s) and the source are credited.

Appendix 1 See Table6.Appendix 2 See Table7.

Table 6List of variables used in the analysis Socio-demographic variables (at or during pregnancy) Two dummies for housing tenure which take the value 1 if the mother owned the house or rented the house during pregnancy (omitted category is social housing); the number of rooms in the house during pregnancy; neighborhood indicators with higher values indicating a better neighbourhood; a dummy indicating the mother’s race (white, with omitted category nonwhite); three dummies indicating the marital status of the mother at the time of pregnancy (married, cohabiting, single/ separated/divorced); ve dummies indicating the mother’s and father’s education level (university degree; A levels (school quali cations obtained at age 18); O levels (school quali cations obtained at age 16); CSE (a lower level of school quali cations obtained at age 16) and vocational); and an indicator variable that takes the value 1 if the mother was working at 18 weeks of pregnancy. Table 6continued Pregnancy and delivery information A dummy that takes value 1 if the child is a female; a dummy that takes value 1 if the child is a twin; mother’s age at birth; an indicator variable that takes value 1 if the mother had a cesarean section; the length of the gestation period.

Health variables Dummy variables for different physical health levels; number of cigarettes smoked each day measured at 32 weeks of pregnancy; number of alcoholic beverages a day before pregnancy; and antenatal EPDS measured at 18 and 33 months pregnancy.

Interpersonal relationships, personality, and stressful life events Dragona’s et al. (1992) measure of the mother’s social network availability; Quinton and Rutter’s (1988) aggression and affection scores for marital quality; a psychological measure of the mother’s personality: the adult version of the Nowicki- Strickand locus of control scale (Duke and Nowicki, 1973); Barnett et al.’s (1983) Life Events Score; an indicator variable that takes the value 1 if pregnancy was unplanned; an indicator variable that takes value 1 if the mother was in local authority care; an indicator variable that takes value 1 if she had divorced parents by age 17; an indicator variable that takes value 1 if the mother’s main carer died by age 17; Table 7Socio-demographic characteristics of study population Units Mean (Std.

error) Pregnancy and birth Gestation in weeks Weeks 39.47 (1.8) Mother’s age at birth Years 28.34 (4.8) C-section 0/1 0.09 (0.3) Primiparous 0/1 0.45 (0.5) Mother works at 18 weeks 0/1 0.55 (0.5) Cigarettes at 32 w No. 2.00 (5.1) Previous alcohol consumption No. 2.59 (0.8) Child characteristics at birth Female 0/1 0.49 (0.5) Twin 0/1 0.01 (0.1) Birth weight grams 3,419.93 (543.9) Head circumference inches 34.84 (1.4) Crown-heel length inches 50.52 (2.2) Demographic and socio-economic variables White mother 0/1 0.95 (0.2) Mother cohabiting 0/1 0.20 (0.4) Mother single 0/1 0.04 (0.2) Owner occupier 0/1 0.74 (0.4) Matern Child Health J (2015) 19:897–907905 123 References 1. O’Hara, M., & Swain, A. (1996). Rates and risk of postpartum depression: a meta-analysis.International Review of Psychiatry, 8(1), 37–54.

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